Method for treating the flanges of containers

ABSTRACT

Containers of synthetic plastic material having an outwardly extending flange about at least a portion of their periphery are subjected to an abrading operation along the outer edge of the flange and then to a brushing operation along the surface of the flange adjacent to the outer edge. To avoid contamination of the interior of the container by the abraded and other plastic particles, desirably air or other gas is caused to flow outwardly across the surfaces of the flange during the abrading and brushing steps.

United States Patent Inventor Richard James Morcom West Hartford, Conn.App]. No. 784,297 Filed Dec. 13, 1968 Patented Jan. 11, 1972 AssigneeMonsanto Company St. Louis, Mo.

METHOD FOR TREATING THE F LANGES OF CONTAINERS 12 Claims, 8 DrawingFigs.

US. Cl 51/323, 51/5, 29/527.2 Int. Cl B24b l/00, B24b 7/00, B24b 9/00Field of Search 51/4, 5,

[56] References Cited UNITED STATES PATENTS 2,494,710 l/1950 Knowlton51/4 101,479 4/1870 Lions 51/4 2,202,372 5/1940 Botera.... 51/2732,831,782 4/1958 Zvanot 29/527.2X 3,400,449 9/1968 Maguire et al. 51/323X 2,958,163 11/1960 Cammerzell 51/5 Primary Examiner-James L. Jones, Jr.Attorneys-H. B. Roberts, James C. Logomasini, Michael J.

Murphy and Peter L. Costas ABSTRACT: Containers of synthetic plasticmaterial having an outwardly extending flange about at least a portionof their periphery are subjected to an abrading operation along theouter edge of the flange and then to a brushing operation along thesurface of the flange adjacent to the outer edge. To avoid contaminationof the interior of the container by the abraded and other plasticparticles, desirably air or other gas is caused to flow outwardly acrossthe surfaces of the flange during the abrading and brushing steps,

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METHOD FOR TREATING THE FLANGES OF CONTAINERS BACKGROUND OF THEINVENTION In recent years there has been ever-increasing utilization ofthermoformed containers of synthetic plastic material for variouspackaging applications. Among the most widely utilized container formsare trays which may be overwrapped with a film of synthetic plasticmaterial to provide an attractive and hygienic container affording theopportunity to display the goods either partially or in their entiretyif the tray is formed of a transparent material.

As is well known, various techniques are employed for the thermoformingand finishing of the containers from the basic sheet stock. From thestandpoint of speed and economy of operation, the therrnoformingtechnique which has achieved very widespread application involves theforming of the container depressions in a long length of the sheetmaterial at one stage, usually several across the width of the sheetmaterial, by means of multicavity dies, and the use of the web betweenthe container cavities to carry the partially formed containers to asubsequent stage where the sheet material is treated to separate thecontainer from the web of material about them. Generally, the formingdies also include cooperating surfaces providing a cutting knife edgeand bed to cut substantially through the thickness of the syntheticplastic material so that the tray forms may be separated from the web ata subsequent stage simply by flexing the sheet material or otherwiseapplying a separating pressure.

Since the cutting dies tend to wear and since the material is, in fact,not cut through cleanly at the time of separation, there is a tendencyfor the crushing and fracturing to produce jagged edges and featherywhiskers of the synthetic plastic along the edge or flange of thecontainer, which render it unsightly. This tendency is particularlypronounced when the material is biaxially oriented to achieve greatstrength at relatively low cost per pound of material. The jagged edgeof the container represents a potential problem in that it maysubsequently cut through a film overwrapped about the container and itand the whiskers may be unpleasant to the touch of the customer.Moreover, particles of plastic adjacent the edge may contaminate thecontents of the container or provide a gritty feel to the customer.

It will be appreciated that the problems of slivers or crushing may beavoided by hot die or wire cutting but such a step would involveelimination of the web as a carrier for the many container units beingformed or additional equipment of substantial complexity and cost andthe likelihood of an increase in overall process time. Thus, it can beseen that any additional steps to be performed on the trays aredesirably performed outside of that type of existing thermoforrningequipment which makes use of the web of the sheet material as a carrierfor the molded container and at a speed sufficient to avoid any delay inhigh-speed or in-line thermoforming operatrons.

It is an object of the present invention to provide a novel method fortreating the flanges of synthetic plastic containers so as to provide asubstantially smooth outer edge and which method is adapted tohigh-speed operation.

It is also an object to provide such a method which also removes anysynthetic plastic particles formed by the separating and formingoperations and deposited on the surfaces of the flange adjacent theother edge.

Another object is to provide such a method in which a multiplicity ofcontainers may be so treated in nested relationship at high speed andwith a relatively high degree of economy. SUMMARY OF THE INVENTION Ithas now been found that the foregoing and related objects may be readilyattained by a method wherein a container having a laterally projectingflange about at least a portion of the periphery thereof is subjected toa series of steps in which the outer edge of the flange is abraded toremove projecting portions of synthetic plastic material therefrom suchas jagged edges and whiskers. Thereafter the surface of the flangeadjacent the abraded outer edge is brushed to remove abraded and othersynthetic plastic particles therefrom. To minimize contamination of thecontainer by abraded and other synthetic plastic particles andfacilitate operation, most desirably a gas is caused to flow outwardlyacross the surface of the flange concurrently with the abrading andbrushing steps.

The technique of the present invention is readily adapted to thetreatment of a multiplicity of trays stacked in nested relationship withspacing between their flanges. It may be effected by passing the traysvertically by the abrading and brushing stations, or most desirably bypassing them in a horizontal path thereby. To provide an even smootherfeel to the flange, a very thin coating of an oil is desirably appliedto the surface thereof following the abrading and brushing operations.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of apparatusembodying the present invention and showing stacks of trays at variouspoints along the flow path through the apparatus:

FIG. 2 is a partially diagrammatical, side elevational view of the firstsection of the apparatus for abrading and brushing the trays;

FIG. 3 is a partially diagrammatical top view of the abrading apparatuswith the housing in section and showing the abrading wheel acting uponan edge of the flanges of a stack of trays;

FIG. 4 is a similar view of the brushing apparatus acting upon thesurface and edges of the flanges of a stack of trays;

FIG. 5 is a partially diagrammatical, fragmentary side elevational viewof the second section of the apparatus showing the brushing andlubricant application stages;

FIG. 6 is a fragmentary sectional view to an enlarged scale of a singletray showing the flange with a typical rough edge and particles on itssurfaces;

FIG. 7 is a similar view showing the flange after the abrading step; and

FIG. 8 is a similar view after the brushing and lubricant applicationsteps with the lubricant film in exaggerated thickness for purpose ofillustration.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Turning now in detailto the attached drawing, FIG. 1 illustrates apparatus embodying thepresent invention which permits treatment of all four sides of stacks oftrays generally designated by the numeral 10. As best seen in FIGS. Sand5, the individual trays are generally designated by the numeral 12 andare of generally rectangular cross section with a flange 14 extendinglaterally outwardly about the periphery thereof but greatly reduced inwidth or eliminated entirely at the rounded comers. As seen in FIG. 6,the tray has a bottom wall 16 and a sidewall 18 extending upwardly at anangle therefrom with the laterally extending flange 14 at the upper endthereof. To provide a spacing between the flanges 14 of adjacent trays12, the sidewall 18 is provided with a stepped portion 19 adjacent thecorner which provides a shelf seating the base of the overlying tray 12.Details of preferred tray configurations are set forth in copending US.Pat. application, Ser. No. 684,417, filed Nov. 20, 1967, by Donald W.Donovan, and assigned to the same assignee as the present invention.

The illustrated apparatus is generally comprised of threeright-angularly disposed conveyor sections A, B and C preceded by a feedtable 20 and followed by a discharge table 22. Initially, a multiplicityof trays 12 is provided as a stack 10 on the feed table 20, eithermanually or preferably automatically, and caused to bear against theback plate 23 to effect alignment thereof. As best seen in FIG. I, thefeed table 20 provides a trifurcated bed with channels 21 thereinextending parallel to the back plate 23. In this embodiment, theconveyor sections A, B and C each include a continuous conveyor,generally designated by the numeral 24, provided by three bands 26spaced apart to provide channels 28 therebetween and rotating on pulleyunits 30 driven by suitable means (not shown).

Disposed within the conveyor belts 24 are pusher units generallydesignated by the numeral 32 and each comprised of a continuous belt 34driven by pulley units 36 synchronously with the conveyor belts 24.Spaced along the length of the belts 34 and supported thereon in aposition generally perpendicular thereto are pairs of rods or fingers 38which project upwardly through the channels 28 between the bands 26 ofthe conveyor belts 24. As the continuous belt 34 of the pusher unit 32of the conveyor section A rotates, its rods or fingers 38 pass throughthe channels 21 of the bed of the feed table 21) and engage the side ofthe stack of trays thereon moving it from the surface of the table 20and onto the conveyor belt 24.

As the stack 10 of trays is moved along by the conveyor belt 24 andpusher unit 32, it passes through a burnishing section comprised of apair of burnishing units each generally designated by the numeral 40.The burnishing unit 40 includes a housing 42 with an elongated aperture44 in its inner face adjacent the conveyor belt 24 and a brush or wheel46 of abrasive material rotating about an axis perpendicular to theconveyor belt 24 and having a portion of its periphery extendingoutwardly through the aperture 44 in the housing 42 so as to contact theouter edge of the flanges 14 of the trays 12 in the stack 10 passingthereby. As best seen in FIG. 3, the abrasive wheel 46 polishes theouter edge of the flanges 14 to smooth the jagged edge and removewhiskers or other particles 48 of plastic therefrom, and the abradedmaterial is carried into the housing by the rotation of the wheel 46which is opposite to the path of movement of the conveyor belt 24. Thehousing 42 is a substantially airtight enclosure with the wheel 46 andaperture 44 being cooperatively dimensioned and configured to minimizethe spacing therebetween. A fitting 50 on the housing is connected to asuitable source of vacuum or negative pressure (not shown) which causesair to flow over the surface of the flanges l2 and into the aperture 44,thus minimizing any tendency for abraded particles to pass into theinterior of the trays 12 or to be scattered into the atmosphere. Theabraded particles will generally be conveyed by the stream of airthrough the fitting 50 and the stream of air is passed through suitablemeans for removing particulate matter (not shown) such as a bag-typefilter or cyclone separator.

In this operation, it can be seen that the fingers 38 are providingpositive driving action against the trailing side of the stack 10 oftrays 12, thus counteracting the pressure of the wheels 46 provided bytheir rotation in the opposite direction and moving them forwardly inproper timed sequence and disposition. Moreover, both sides of the stack10 are being acted upon simultaneously so that displacement transverselyof the belt 24 is avoided. It is important that the burnishing wheels 46and the stack 10 of trays be properly aligned so that only the desiredamount of surface of the flanges 14 is removed. To this end, the backplate 23 is desirably adjustable to provide the initial adjustedposition for the stack 10 and the pair of fingers 38 maintains thisposition; similarly, the burnishing units 40 may be adjustably mountedon the frame 41 of the apparatus.

After the burnishing section, the stack 10 of trays passes to thebrushing section comprised of a pair of brushing units generallydesignated by the numeral 52 mounted on the apparatus frame 41 and eachhaving a housing 54 with a brush 56 rotating therein about an axisperpendicular to the conveyor belt 24. As best seen in FIG. 4, thehousing 54 has an elongated aperture 58 in its inner face adjacent theconveyor belt 24 and the brush 56 has filamentary or bristlelikeelements 60 defining its periphery and which project outwardly throughthe aperture 58 so as to project inwardly of the outer edges of theflanges 14 between the trays 12. Since the brushes 56 are rotating in adirection opposite to the path of movement of the stack 10 of trays 12,the bristlelike elements 60 remove any synthetic plastic particles 48thereon and propel them into the housing 54. Again, contamination issubstantially avoided and movement of the particles 48 into the housing54 is facilitated by the flow of air across the surfaces of the flanges14 as a result ofa source vacuum or negative pressure connected to thefitting 62 on the housing 56.

As the conveyor belt 24 continues to carry the stack 10 of trays, thepath of movement brings the stack 10 against the stop plate 64 at theend of the conveyor section A and the stack 10 strikes the limit switch66 thereon actuating the transfer unit generally designated by thenumeral 68. In the illustrated embodiment, the transfer unit 68 isgenerally disposed above the conveyor belts 24 of the conveyor sectionsA and B and includes a vertically extending pusher plate 70 supported onthe piston rod 72 which reciprocates within the piston cylinder 74operated by air or other suitable fluid medium from a source (not shown)and controlled by the limit switch 66 to drive it to thepiston-retracted position and then automatically returned to thepiston-extended position shown in FIG. 1 of the drawings. The movementof the pusher plate 70 is stabilized by the shafts 76 which are slidablysupported in the blocks 78 of the transfer unit 68. When the pistoncylinder is operated by the limit switch 66, the pusher plate 70 abutsagainst the side of the stack 10 of trays and pushes the stack 10 fromthe conveyor belt 24 of the section A onto the con veyor belt 24 of thesection B.

The conveyor belt 24 of the conveyor section B now begins to carry thestack 10 of trays 12 along the length thereof. The fingers 38 of thepusher units 32 move into engagement with the trailing edge of the stack10 prior to its passage between the burnishing units 40 so as to providethe desired positive driving pressure therebehind. From the burnishingunits 40, the stack 10 then passes between the brushing units 52 andstill further along the length of the conveyor belt until it reaches thelubricant application section comprised of a pair of applicator unitsgenerally designated by the numeral 80. Although various types ofapplicator units may be employed, the illustrated embodiment utilizes aroller 82 mounted for rotation about a vertical shaft and having anabsorbent outer surface and an internal cavity (not shown) into whichthe lubricant is fed from an external source (not shown). The flexiblecharacter of the absorbent covering on the roller 82 permits it to applya thin film of the lubricant over the surfaces of the flanges 14 of thetrays 12 for some distance inwardly of the outer edge thereof. In FIG.8, the lubricant film bears the numeral 90.

The continuing movement of the conveyor belt 24 causes the stack to abutagainst the stop plate 84 and strike the limit switch 66 producingactuation of the transfer unit 68 constructed and operating similarly tothat previously described. This, in turn, results in movement of thestack 10 of trays 12 from the conveyor belt 24 of the section B onto theconveyor belt 24 of the section C. Again, pusher fingers 38 of thepusher unit 32 abut against the trailing edge of the stack 10 to providepositive driving engagement between the rollers 82 of the applicatorunit which is constructed and operates similar to that previouslydescribed to provide a thin film of lubricant along the surfaces of theflanges 14 at the previously untreated sides. Lastly, the conveyor belt24 discharges the stack 10 onto the discharge table 22 from which it maybe transferred either manually or automatically.

The process and apparatus of the present invention are applicable tocontainers formed of various synthetic plastics and preferablythermoplastics. Exemplary materials are the polyolefins such aspolyethylene, ethylene-propylene copolymers and isotactic polypropylene,polyacrylates, polymethacrylates, polycarbonates, polyvinyl chloride,polyethylene terephthalates and styrene polymers. The preferredthermoplastics are styrene polymers such as biaxially orientedpolystyrene, impact polystyrene, ABS and styrene/acrylonitrilecopolymers. Of the various styrene polymers, biaxially orientedpolystyrene is most desirably utilized because of its excellenttoughness and resilience even in thin sections and because of itsrelatively inert qualities with respect to foods and other materials.

Most usually, the containers will be thermoformed from synthetic plasticsheet material in order to achieve fabrication at the greatest possiblerates of speed and with the greatest economy. The actual configurationof the container and of the flange is not critical since the apparatusand process may be modified to accommodate substantially any type ofconfiguration. However, for most facile operation, the container willnormally be polygonal and preferably rectangular in cross sectionalthough it may have rounded corners as in the illustrated embodiment.The technique of the present invention is also applicable toinjection-molded or blow-molded containers to remove flash and otherprojecting portions about any flange provided thereon.

The bumishing units may utilize various types of abrasive membersincluding wheels or rollers of the type illustrated or belts of abrasivematerial operating about pulleys. Generally, the periphery of theabrading element should be well defined in order to provide closecontrol over the amount of surface being abraded; however, someresiliency in the surface of the element may be provided such as in aflap wheel using abrasive-impregnated cloth flaps mounted on a core. Theabrading element also may be provided by an abrasive-filled syntheticplastic material or simply by abrasive material bonded to a suitablesupport surface.

Since it is desirable for the brushing elements to penetrate somewhatinwardly of the abraded outer edge to effect removal of the syntheticplastic particles lying on the surface of the flanges, the brushespreferably employ flexible filamentary or bristlelike elements whichwill deform about and penetrate between the flanges of adjacent trays todislodge and propel the particles outwardly therefrom. Bristle brusheshave proven particularly advantageous for this purpose, and the bristlesmay be natural or synthetic plastic.

Instead of the apertured housings shown in the illustrated embodimentwhich facilitate the flow of air across the surface of the flanges, itis possible to utilize larger enclosures providing ducts or hoodsadjacent the bumishing and brushing elements which are connected to fansor vacuum units of sufficient capacity so as to produce the desired airflow across the surface of the flanges. Generally, the illustratedarrangement minimizes the amount of air flow required to achieve thedesired purpose and thereby the resultant amount of air which must betreated so as to remove the entrained synthetic plastic particles. Inanother type of apparatus, positive air pressure may be utilized to blowacross the surfaces on the flanges and into a duct or hood arrangementcooling the synthetic plastic particles.

From the standpoint of applicators for the lubricant, various devicesmay be employed in addition to the roller provided with an internalcavity heretofore described. For example, a pair of rollers may beemployed, the first being highly absorbent and abutting against theactual applicator so as to transfer lubricant from its surface to theabsorbent surface of the applicator. The first roller may then besupplied with lubricant by dripping, spraying or otherwise, and theamount transferred from the first roller to the applicator will bedependent upon the pressure at the nip and the relative absorbency ofthe two surfaces. It will also be appreciated that lubricant may besupplied to the applicator surface directly by spraying or drippingthereonto.

Various types of lubricants may be employed to provide a smooth feel tothe user including silicone oils, polyethylene glycol, vegetable oilsand various natural and synthetic waxes. If the viscosity of thelubricant is sufficiently high, it may be desirable to employ a solventsolution thereof which will deposit the desired film. Generally, thelubricant should form a very thin coating on the order of less than atenth of a mil and preferably less than 0.05 mil.

It will be appreciated that various types of conveyors and pusherarrangements may be employed to effect the desired movement of the traysthrough the bumishing and brushing stations. For example, the trays mayslide on a fixed conveyor bed and be moved therealong by an overheadpusher unit or the pusher unit may have fingers projecting upwardlythrough the fixed slide bed. If automatic or semiautomatic operation isnot required, trays may be moved manually through the bumishing andbrushing stations. Instead of the three-section conveying apparatusillustrated, the apparatus may eliminate one section by providing alubricant application station along the first section after the brushingstation; the stacks of trays may then be discharged from the secondconveying section onto the discharge table.

It can be seen that the present invention readily adapts itself tohigh-speed operation either in conjunction with high-speed thermoformingunits producing containers for packaging and shipment elsewhere or inline with the actual packaging installations. The method and apparatusare relatively economical and are operable independently of the formingequipment so as to provide considerable versatility and adjustability tocontainers of various configurations and dimensions.

What is claimed is:

1. In a method for treating containers of synthetic plastic material thesteps comprising: stacking a multiplicity of containers of syntheticplastic material having a laterally projecting flange about at least aportion of the periphery thereof in nested relationship with spacingbetween the flanges thereof; abrading the outer edge of said flanges ofsaid stack of containers to remove projecting portions of syntheticplastic material therefrom; brushing the surface of said flanges of saidstack at said abraded outer edge thereof to remove abraded and othersynthetic plastic particles therefrom; and concurrently with saidabrading and brushing steps causing a gas to flow outwardly across saidflange adjacent said abraded outer edge to minimize contamination of theinterior of said containers by abraded and other synthetic plasticparticles.

2. The method in accordance with claim I wherein said synthetic plasticmaterial is biaxially oriented and wherein said containers arethermoformed from said synthetic thermoplastic sheet material.

3. The method in accordance with claim 1 wherein said containers are ofgenerally rectangular cross section and wherein said abrading andbrushing steps are concurrently conducted with respect to flanges alongopposite sides thereof.

4. The method in accordance with claim 3 wherein similar abrading andbrushing steps are subsequently conducted with respect to the remainingsides of the container.

5. The method in accordance with claim 1 wherein said gas is drawnoutwardly across said flange by means of negative pressure.

6. The method in accordance with claim 1 wherein a thin film oflubricant is applied to the surface of said abraded flanges subsequentto said abrading and brushing steps to provide a smooth slippery feelthereto.

7. The method in accordance with claim 1 wherein said containers are ofgenerally rectangular cross section, wherein a multiplicity ofcontainers are disposed in nested relationship with spacing between theflanges thereof and the brushing action extends inwardly from the outeredge of said flanges and between said flanges, and wherein said abradingand brushing steps are concurrently conducted with respect to flangesalong opposite sides thereof.

8. The method in accordance with claim 7 wherein similar abrading andbrushing steps are subsequently conducted with respect to the remainingsides of the containers.

9. The method in accordance with claim 7 wherein a thin film oflubricant is applied to the surface of said abraded flanges subsequentto said abrading and brushing steps to provide a smooth slippery feelthereto.

10. The method in accordance with claim 1 wherein said brushing actionis provided by a brush rotating on an axis parallel to the height ofsaid stack of containers.

11. The method in accordance with claim 10 wherein said brush rotates ina direction opposite to the direction of relative movement between saidstack of containers and said brush.

12. The method of claim I wherein said brushing action extends inwardlybetween the flanges of said stacks to remove particles from the edgeportions adjacent said outer edges.

1. In a method for treating containers of synthetic plastic material thesteps comprising: stacking a multiplicity of containers of syntheticplastic material having a laterally projecting flange about at least aportion of the periphery thereof in nested relationship with spacingbetween the flanges thereof; abrading the outer edge of said flanges ofsaid stack of containers to remove projecting portions of syntheticplastic material therefrom; brushing the surface of said flanges of saidstack at said abraded outer edge thereof to remove abraded and othersynthetic plastic particles therefrom; and concurrently with saidabrading and brushing steps causing a gas to flow outwardly across saidflange adjacent said abraded outer edge to minimize contamination of theinterior of said containers by abraded and other synthetic plasticparticles.
 2. The method in accordance with claim 1 wherein saidsynthetic plastic material is biaxially oriented and wherein saidcontainers are thermoformed from said synthetic thermoplastic sheetmaterial.
 3. The method in accordance with claim 1 wherein saidcontainers are of generally rectangular cross section and wherein saidabrading and brushing steps are concurrently conducted with respect toflanges along opposite sides thereof.
 4. The method in accordance withclaim 3 wherein similar abrading and brushing steps are subsequentlyconducted with respect to the remaining sides of the container.
 5. Themethod in accordance with claim 1 wherein said gas is drawn outwardlyacross said flange by means of negative pressure.
 6. The method inaccordance with claim 1 wherein a thin film of lubricant is applied tothe surface of said abraded flanges subsequent to said abrading andbrushing steps to provide a smooth slippery feel thereto.
 7. The methodin accordance with claim 1 wherein said containers are of generallyrectangular cross section, wherein a multiplicity of containers aredisposed in nested relationship with spacing between the flanges thereofand the brushing action extends inwardly from the outer edge of saidflanges and between said flanges, and wherein said abrading and brushingsteps are concurrently conducted with respect to flanges along oppositesides thereof.
 8. The method in accordance with claim 7 wherein similarabrading and brushing steps are subsequently conducted with respect tothe remaining sides of the containers.
 9. The method in accordance withclaim 7 wherein a thin film of lubricant is applied to the surface ofsaid abraded flanges subsequent to said abrading and brushing steps toprovide a smooth slippery feel thereto.
 10. The method in accordancewith claim 1 wherein said brushing action is provided by a brushrotating on an axis parallel to the height of said stack of containers.11. The method in accordance with claim 10 wherein said brush rotates ina direction opposite to the direction of relative movement between saidstack of containers and said brush.
 12. The method of claim 1 whereinsaid brushing action extends inwardly between the flanges of said stacksto remove particles from the edge portions adjacent said outer edges.